296 
JOURNAL OF ECONOMIC ENTOMOLOGY 
[Vol. 16 
Cause of Resistance 
Since the results of the field and greenhouse tests indicated that 
certain varieties of wheat were more resistant to the Hessian fly than 
others, the next step to be considered was the cause of resistance. 
During the past two years, much of the investigational work has been 
along this line. As there was no apparent discrimination by the adults 
in ovipositing, it w r as assumed that resistance was due to morphological 
or physiological characters of the plant. Preliminary experiments 
were, therefore, started to determine (1) the ability of the larvae on 
hatching to get down to their normal feeding place at the base of the 
plant, and, (2) their ability to rasp the stem and begin feeding. A 
large series of tests was made with selected varieties of the migration 
of the larvae and the results are summarized in Table II. 
Table II— Showing the Percentage of Larvae that are able to Reach Their Normal Feeding 
Place on the Different Varieties 
Variety 
Number 
Kind 
No. of 
tests 
Total 
No. lar¬ 
vae 
No. of 
larvae 
getting 
down 
Per cent 
of larvae 
getting 
down 
Marquis. 
Spring 
23 
469 
377 
SO.3 
Kanred. 
2401 
Hard Red Winter 
35 
1084 
626 
57.7 
Turkey. 
2407 
it It 11 
26 
564 
399 
70.7 
Red Winter. 
2101 
it it it 
43 
1148 
671 
58.4 
Red Winter. 
2132 
11 it a 
31 
649 
422 
65.0 
Kharkof. 
382 
a a a 
24 
383 
305 
79.6 
Turkish Hybrid. 
196 
a a n 
27 
478 
282 
59.0 
Zimmerman. 
2084 
Soft Red Winter 
27 
684 
404 
59.0 
Currell Selection. 
2406 
a a a 
23 
451 
339 
75.1 
Beechwood Hybrid . 
100 
a tt a 
1 
34 
11 
32.3 
Illini Chief. 
3278 
a a a 
5 
372 
159 
42.7 
a it 
3291 
a a a 
18 
714 
445 
62.3 
it a 
2591 
a 11 11 
54 
1714 
875 
51.0 
Illini Chief 
x Kanred. 
223x 
2401 
5 
203 
104 
51.2 
Illini Chief Sel. 
x Kanred Sel. 
223x 
2401 
14 
1465 
443 
30.2 
Dawson Golden Chaff. 
78 
Soft White Winter 
23 
611 
187 
30.6 
The results shown in this table may be summarized as follows: (1) 
There is a high mortality between the time of hatching and that of reach¬ 
ing the base of the plant on all varieties. (2) There is a marked difference 
in the percentage of larvae getting down on the different wheats, rang¬ 
ing from 30 percent for Dawson Golden Chaff and certain Illini Chief 
